All animals excrete feces
am Puls Biologie 5, textbook
98 4.2 Excretion in the animal kingdom Excretion: Excretion of waste products of the metabolism Excretion Why do toxic waste materials arise at all? The digestive system only absorbs what is usable from food. How can it be that something harmful emerges from this? Carbohydrates and fats (which only consist of the elements carbon, hydrogen and oxygen) can be completely broken down into water and CO 2 - no poison is produced here. CO 2 is exhaled and water is the main component of the cells anyway. Protein metabolism is more problematic: Proteins consist of various amino acids, all of which contain nitrogen. When amino acids are restructured and broken down (and, to a lesser extent, other N-containing substances), part of the nitrogen remains - in the form of ammonia (NH 3). In aqueous solution, ammonia turns into ammonium ion (NH 4 +), a strong cell poison that must be quickly removed from the body. Most aquatic animals secrete the water-soluble ammonium directly through their skin and gills (k Fig. 4). Land animals cannot do this, they have to use water sparingly. You eliminate this poison by producing urea or uric acid. Urea is much more harmless than ammonium, but it still has to be continuously released with water (through the urine). Uric acid is less of a problem and is stored in large quantities in the egg by the bird embryo, for example. The white pulp around the bird droppings also consists of v. a. from uric acid. Ammonia is a poisonous waste product and can be excreted as ammonium, urea or uric acid. Fig. 4: Excreta in the animal kingdom. Ammonia, which comes from the amino acid metabolism, is a strong cell poison. The task of excretion is to excrete this substance directly (as ammonium) or to convert it into other substances, which are then excreted. Conversion into urea Conversion into uric acid degradation processes Ammonia (NH 3) as a by-product Ammonium ion Excretion Excretion Excretion Bone fish Mammals, amphibians Reptiles, insects, birds Amino acids, nucleotides The disposal of metabolic waste from the body is called excretion. This process takes place in three steps, which are illustrated by the following comparison: Imagine that your room is in total chaos. First, put all the items lying around in a large box - this corresponds to filtration. In a second step, you check the items in the box again and take out everything you want to keep - this corresponds to reabsorption. In the last step you empty the remaining contents of the box into the garbage container - that is the elimination of the waste materials. All three processes together correspond to the excretion in the body of animals. But why is excretion necessary at all? Just as a mess often arises in our rooms during times of intensive work, this also happens in cells: In the course of metabolism, various substances accumulate in the body fluids. Some of them (eg ammonia) are harmful and must be removed from the body before they can cause harm. Others (eg sugar) are too valuable to be excreted. These materials must not be lost and must therefore be retrieved. Excretion must not be confused with excrement: excrements are the indigestible remains of food that leave the intestine as feces. Excreta, on the other hand, are substances that arise as waste in the body during metabolism and must be disposed of. Hence there are two separate systems, we excrete feces (as excrement) and urine (as excrement). The metabolism produces waste materials that have to be removed from the body. For testing purposes only - property of the publisher öbv
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